class Solution {
public:
    int minDistance(string word1, string word2) {
        int n1 = word1.size(), n2 = word2.size();
        vector<vector<int>> dp(n1 + 1, vector<int>(n2 + 1));
        for(int i = 1; i <= n1; ++i)
        {
            dp[i][0] = i;
        }
        for(int j = 1; j <= n2; ++j)
        {
            dp[0][j] = j;
        }

        for(int i = 1; i <= n1; ++i)
        {
            for(int j = 1; j <= n2; ++j)
            {
                if(word1[i - 1] == word2[j -1])
                    dp[i][j] = dp[i - 1][j - 1];
                else
                    dp[i][j] = 1 + min(min(dp[i - 1][j], dp[i][j - 1]), dp[i - 1][j - 1]);
            }
        }
        return dp[n1][n2];
    }
};